In Japanese Unexamined Patent Application Publication No. 2006-521022 (Patent Document 1), a substrate is disclosed in which a conductive or semi-conductive substrate is divided into a plurality of partial regions by a trench extending through the substrate and the foregoing partial regions are used as electrically connecting members. In Japanese Unexamined Patent Publication No. 2008-229833 (Patent Document 2), a semiconductor device is disclosed in which the same substrate as described above is used as a cap substrate opposing a base substrate and bonded thereto and a predetermined one of the partial regions mentioned above functions as a conductive region extracted from the base substrate.
FIGS. 32A and 32B show an example of the semiconductor device disclosed in Patent Document 2, of which FIG. 32A is a schematic cross-sectional view of a semiconductor device 91 and FIG. 32B is a schematic top view of the semiconductor device 91. The cross-sectional view of FIG. 32A shows a cross section along a dash-dot line XXXIIA-XXXIIA of FIG. 32B, which is arbitrarily extended/contracted along the section line and simplified for clear illustration. Note that, in FIG. 32B, a movable electrode Em and a stationary electrode Es in the semiconductor device 91 are shown in a simplified manner, but actually have comb-like shapes to be interdigitated.
FIGS. 33A and 33B are views showing a base substrate B2 of the semiconductor device 91 of FIGS. 32A and 32B, of which FIG. 33A is a cross-sectional view of the base substrate B2 and FIG. 33B is a top view of the base substrate B2. FIGS. 34A and 34B are views showing a cap substrate C2 of the semiconductor device 91 of FIGS. 32A and 32B, of which FIG. 34A is a cross-sectional view of the cap substrate C2 and FIG. 34B is a top view of the cap substrate C2. Note that, in FIGS. 32A to 34B, the cross-sectional views of FIGS. 32A, 33A, and 34A correspond to each other, and the top views of FIGS. 32B, 33B, and 34B correspond to each other. Also, in FIGS. 32A to 34B, the section lines shown by the dash-dot lines XXXIIA-XXXIIA correspond to each other.
The semiconductor device 91 shown in FIGS. 32A and 32B has the base substrate B2 made of a semiconductor, and the cap substrate C2 having electrical conductivity to be bonded to the base substrate B2.
As shown in FIGS. 33A and 33B, the base substrate B2 in the semiconductor device 91 of FIGS. 32A and 32B is a SOI (Silicon On Insulator) substrate having a buried oxide film 20, and includes a SOI layer 21 and a support substrate 22 between which the buried oxide film 20 is interposed. In the surface layer portion of the base substrate B2, a plurality of dielectrically isolated base semiconductor regions Bs are formed. That is, the base semiconductor regions Bs of the semiconductor device 91 are each formed of the SOI layer 21, and dielectrically isolated from the surroundings by trenches 23 reaching the buried oxide film 20.
The semiconductor device 91 has dynamic quantity sensor elements each using an inertial force, and the dynamic quantity sensor elements each for measuring an acceleration or an angular velocity are formed of the plurality of base semiconductor regions Bs formed in the surface layer portion of the base substrate B2 in a predetermined region R1 of the base substrate B2. That is, of the plurality of base semiconductor regions Bs in the base substrate B2, base semiconductor regions Bs1 shown in the drawings serve as movable semiconductor regions having movable electrodes Em formed to be displaceable by sacrificially etching part of the buried oxide film 20. On the other hand, the other base semiconductor regions Bs2 shown in the drawings serve as stationary semiconductor regions having stationary electrodes Es opposing the movable electrodes Em. Note that the two movable semiconductor regions Bs1 and the two stationary semiconductor regions Bs2 which are shown in the cross-sectional view of FIG. 33A form respective integrally coupled regions in a two-dimensional configuration, as shown in FIG. 33B. In the semiconductor device 91, the opposing surfaces of the movable electrode Em of the movable semiconductor regions Bs1 and the stationary electrode Es of the stationary semiconductor regions Bs form an electrostatic capacitance. The movable electrode Em is displaced in a direction perpendicular to the opposing surfaces in accordance with a dynamic quantity applied thereto to measure a change in the electrostatic capacitance resulting from a distance change between the movable electrode Em and the stationary electrode Es, and detect the applied dynamic quantity.
As shown in FIGS. 34A and 34B, the cap substrate C2 in the semiconductor device 91 of FIGS. 32A and 32B is formed of a single-crystal silicon substrate 30, and a plurality of cap conductive regions (partial regions) Ce are formed therein. That is, the cap conductive regions Ce in the semiconductor device 91 result from the division of the cap substrate C2 (single-crystal silicon substrate 30) by dielectric isolation trenches 31 extending therethrough. Note that, in the cap substrate C2, the portion denoted by a reference numeral 33 is a surface protective layer formed of a silicon dioxide (SiO2) film or the like, and the portions each denoted by a reference numeral 34 are electrode pads made of aluminum (Al) or the like.
As shown in FIGS. 32A and 32B, in the semiconductor device 91, a projecting portion T1 formed of a conductive film 50 of conductive polysilicon containing an impurity at a high concentration, metal, or the like is formed on the base semiconductor region Bs in the predetermined region R1. The cap substrate C2 is bonded to the projecting portion T1 of the base substrate B2 to form a junction surface D1. The junction surface D1 between the base substrate B2 and the cap substrate C2 is set to be annular in the predetermined region R1 of the base substrate B2. The space formed by the surface of the predetermined region R1 in the base substrate B2 and the surface of the cap substrate C2 as a result of the bonding together of the base substrate B2 and the cap substrate C2 described above is sealed in a high-vacuum state or in a predetermined atmosphere (such as N2) under pressure. By the bonding together described above, predetermined cap conductive regions Ce1 and Ce2 illustrated in the drawing function as extraction conductive regions electrically connected to the predetermined base semiconductor regions Bs2 and Bs2. That is, to the movable semiconductor region Bs1 and the stationary semiconductor region Bs2 in the base substrate B2, the extraction conductive regions Ce1 and Ce2 are connected respectively via the conductive film 50.
The semiconductor device 91 shown in FIGS. 32A and 32B uses the single-crystal silicon substrate 30 as the cap substrate C2 to be bonded in opposing relation to the base substrate B2, and the predetermined cap conductive regions (partial regions) Ce1 and Ce2 function as the conductive regions extracted from the base substrates B1 and B2. The foregoing semiconductor device 91 can be formed as a semiconductor device having reduced mounting restrictions which can be manufactured in a small size at low cost and which allows the dynamic quantity sensor elements formed in the surface layer portion of the base substrate B2 to be sealed and protected by the foregoing cap substrate C2.
Meanwhile, in the foregoing semiconductor device 91, the single-crystal silicon substrate 30 is used as the mother substrate forming the cap substrate C2. Single-crystal silicon is lower in cost than other substrate materials and easier in trench formation. However, since single-crystal silicon has a relatively high specific resistance, it shows a large resistance value when used in an extraction conductive region so that the range of application thereof as an extraction conductive region is limited.    [Patent Document 1] Japanese Unexamined Patent Application Publication No, 2006-521022, corresponding to US 2008/029049    [Patent Document 2] Japanese Unexamined Patent Publication No. 2008-229833, corresponding to U.S. Pat. No. 7,560,802